1. Field of the Invention
This invention relates to a dry flocculant powder composition and method for making the same. The invention further relates to various methods for using the aforementioned flocculant powder to remove colloidal suspensions from waste water streams through filtration, gravity settling and/or centrifugation. The invention rapidly reduces the turbidity of aqueous solutions containing clay and clay-like materials, humic acids, yeast and other biological cell debris.
One of the major problems facing municipalities and most chemical industries today is the proper disposal of waste products. Methods for purifying waste waters, particularly aqueous streams containing organic contaminants, have been the subject of much investigation. Disposal of contaminated solutions is especially problematic for those who treat municipal sewage, industrial water supplies, or discharges from mineral dressing operations, food processing plants, breweries and many other operations. Federal, state and local government regulations have made it illegal to dump certain untreated waters back into the environment.
Various methods have been proposed for removing certain contaminants from an aqueous solution. It is well known to use such water purifying materials as alum, ferric chloride, other ferric- or ferrous-salts, alone or in combination with lime, sodium aluminate, soluble starches and water soluble polymers. The foregoing materials are often limited to use in only certain pH ranges, however. They must also be applied in precise proportion to the solids content of the water being treated, thus making it more difficult to establish means for uniformly removing contaminants from an aqueous stream. When only small amounts of contaminant are present, removal problems become even more complicated.
In many chemical and industrial manufacturing processes, waste water is often recycled. Over time, these waters accumulate environmentally unsafe levels of compounds which, in most cases, are anionic and have an adverse effect on the basic manufacturing process. For example, in the manufacture of paper, compounds such as humic acids, lignin sulfonic acids, and oxidized polysaccharides accumulate in the recycled water of a paper-making machine. Other particularly troublesome contaminants include clay and clay-like materials. These and other impurities are readily found in the ores co-extracted with bauxite. During the recovery of aluminum oxide (or alumina) from bauxite through the well-known Bayer process, some of these undesirable impurities are digested or decomposed to lower molecular weight compounds which will contaminate the various liquor streams associated with the Bayer process. In still other man-made operations, especially those associated with the production of food products, waste water streams are commonly loaded with significant amounts of protein matter, yeast products, amino acids, dyestuffs and/or other biological cell debris. The concentrations of such contaminants must also be significantly reduced before these waters are considered safe for release into the environment.
Aside from man-made pollutants, natural contamination also takes its toll on existing water supplies. Turbid waters often have a haziness caused by insoluble suspended particles such as clay, silt, bacteria, viruses, and even organic debris resulting from the decay of plant life and similar materials present in natural streams or the like. Turbidity standards have been established for determining the quality of water which municipal authorities are allowed to distribute from their facilities. Turbidity measurements are typically made by determining the amount of light scattered by undesirable particulates in a given water sample.
2. Technology Review
Over the years, several different products, methods and apparatus have been developed for handling certain waste water contaminants. The following references are exemplary of this technology.
Pollio U.S. Pat. No. 3,300,406 claims a method for treating water containing an anionic material by introducing to the water, in any order, (i) an inorganic, polyvalent metal salt; (ii) a finely-divided siliceous material; and (iii) a polymeric salt having a molecular weight between 20,000-10 million including a particular carbon-atom backbone chain. The siliceous material selected for separate introduction to the water being treated is preferably water-insoluble and carries a negative electrokinetic charge.
Innes et al U.S. Pat. No. 3,488,718 claims an improved method for separating substantially pure synthetic hydrous oxides which are capable of adsorbing anionic materials from an aqueous suspension. The method comprises adding to the suspension under flocculating conditions a water-soluble polyelectrolyte having a desired formulaic structure, preferably of polycarboxyethylene linkages.
Hedrick et al U.S. Pat. No. 3,516,932 shows a method for clarifying an aqueous clay suspension, in a flocculated state, due to the presence of inorganic salts. The method comprises adding to the suspension up to about 0.1% by weight of a polyacrylamide.
In Ledden et al U.S. Pat. No. 3,707,523, there is claimed a process for making reconstituted landfill from phosphate ore water slimes. The process includes adding polyelectrolyte and sand to these slimes for rapid solidification purposes. Because of susceptibility to damage by agitation, "however, these flocculants are added to the wet sand as a 0.1-0.5% aqueous solution."
Krillic et al U.S. Pat. No. 3,948,784 claims a method for treating an aqueous solution of water-soluble lubricants, said solution including suspended particles of metals, metal oxides, silica and/or carbon. The method comprises adding at least 0.5 ppm by weight of a cationic polyelectrolyte to the solution; dispersing the polyelectrolyte in said solution; and allowing it to stand for at least two minutes before separating lubricant from the settled particles.
Field et al U.S. Pat. No. 4,043,910 shows a method for removing phosphates from raw sewage, sewage sedimentation effluent, or food processing effluent containing said phosphates. The process comprises the steps of first precipitating soluble phosphates from the solution through contact with an inorganic coagulant containing aluminum, ferrous, ferric or calcium ions. About 15 seconds to 4 minutes later, a sufficient amount of cationic polyelectrolyte (as formulaically defined therein) is added to the solution before a liquid-solids separation process is practiced.
Olesen et al U.S. Pat. No. 4,076,615 claims an improved process for removing dissolved organic pollutants from waste water. The process includes contacting the water with an oxygen-containing gas and an acidified slurry of activated carbon and alum. The pH of this solution is then adjusted to cause aluminum hydroxide to precipitate before adding a polyelectrolyte flocculant to the water.
Halbfoster U.S. Pat. Nos. 4,177,142 and 4,238,334 show a method and filter bed for removing impurities from a liquid. The bed comprises: (a) a preferably fibrous filter aid material which has been treated with an electrolyte-type compound for producing a surface charge opposite the filter material's normal charge; and (b) an active particulate material having an opposite surface charge from that of the treated filter aid material in aqueous suspension. The particulate material ultimately added to treated filter aid material may be selected from the group consisting of organic polymeric absorbents, zeolites, bentonite, zirconium oxide, zirconium phosphate, activated alumina, ferrous sulfide, activated carbon and diatomaceous earth.
In Gnyra U.S. Pat. No. 4,275,043, there is claimed a method for controlling the level of sodium oxalate in a Bayer liquor stream, said stream containing in excess of 1 g/L of humic matter. The method includes treating the liquor stream with no more than 0.5 g/L of an adsorbent selected from activated carbon, activated alumina or activated clay.
Weiss et al U.S. Pat. Nos. 4,279,756 and 4,363,749 show a coagulant/adsorbent and method for removing suspended impurities from water through coagulation. The preferred adsorbent for this method consists of mineral or clay particulates, with an average size of 10 microns or less, which have a thin hydroxylated surface layer with a positive zeta potential at the pH range set forth therein.
Degen et al U.S. Pat. No. 4,425,238 claims a method for removing acid dyes from recyclable waste water by adding to the water an effective amount of a polymeric cationic assistant made by reacting together an aromatic alkylating agent and a mixture of an aminoalkyl-containing polyelectrolyte with some aluminosilicate, chalk, titanium dioxide, bauxite and/or calcium sulfoaluminate.
Beall U.S. Pat. No. 4,549,966 shows a method for removing from an aqueous composition organic contaminants selected from insoluble organics, aliphatic contaminants, humics and mixtures of the same. The method comprises contacting the contaminated solution with a sufficient amount of an organoclay which was prepared by reacting together a quaternary ammonium salt and a smectite-type clay.
Musselman et al U.S. Pat. No. 4,781,982 shows a method for treating mineral particles such as alumina, bauxite, magnesium, mica, talc, etc., to reduce the adsorption of halide ions and halide-free radicals onto said particles. The method includes surface treating these particles with an alkali metal silicate agent in an aqueous solution having an initial pH of at least 8.5, before neutralizing said solution (to a lower pH), thereby precipitating a silica coating onto said particles.
British Patent No. 1,466,185 shows a method for dewatering aqueous slimes through contact with a solid material having a preferred particle size between 200 microns and 4 mm. Before slime contact, polyelectrolytes are mixed with these particles to cause them to attract clay or reject water at a location sufficiently close to the particles. Such polyelectrolytes do not remain fixedly coated to these large substrate particles. Instead, they leave the surface of these particles and dissolve in a liquid medium for possible recycling.
In British Patent No. 1,512,481, there is claimed a method for removing proteinaceous matter from liquid effluent by adding a flocculant or coagulant to the effluent, then an adsorbent, followed by the addition of a polyelectrolyte. Solid material is then removed from the foregoing mixture through flotation.
British Patent Application No. 2,092,121 shows a process for purifying waste water by: (a) forming floc particles under high shear from a material having a particle size of 10-100 microns, and a high molecular weight polyelectrolyte in the presence of water; then (b) removing suspended solids from the water by treating with these floc particles. According to page 2, lines 43-51, treatment is best effected by passing through a bed of these floc particles.
Canadian Patent No. 1,169,735 claims a process for producing an anionic exchanger by treating cellulose, or a cellulose derivative, with polyethyleneamine in an aqueous reaction medium at a pH between 2 and 6.
West German Patent No. 2,655,356 shows a process for purifying waters containing organics, especially protein and yeast-containing substances. The process includes adding two separate slurries to the water being treated. The first slurry comprises a flocculating agent in the form of a polyelectrolyte, especially polyacrylamide. The second slurry includes an aqueous solution of aluminum oxide and/or silicon dioxide.
West German Patent No. 3,438,140 shows a process for removing heavy metals from waste water by strongly mixing the water under neutral pH conditions with an aqueous sodium aluminate solution in the presence of a polyelectrolyte.
South African Patent No. 7,600,152 claims a method for dewatering colloidally suspended mineral slime and microbial sludge waste, which method includes: adding a fly ash slurry to the waste being treated at a prescribed rate; gently mixing the resulting solution; then adding a polyelectrolyte to this admixture at another prescribed rate followed by more gentle mixing.